[gillesjacobs]

> Did you put any copyright notices in your work? If not, it may be too late, because they can continue to distribute the old version that did not have copyright notices.

This is not how copyright works. Without a license, default copyright law applies, and no one can make any copy of the code and profit from it, even if published on Github. Copyright protection is automatic under the Berne Convention, implemented by the US Copyright Act and EU Directive 2001/29/EC, meaning no registration or notice is required for protection.